Edit in JSFiddle

var treeData=[
    {"id":1,"parentId":null,"title":"1"},
    {"id":2,"parentId":1,"title":"1.1"},
    {"id":3,"parentId":null,"title":"2"},
    {"id":4,"parentId":1,"title":"1.2"},
    {"id":5,"parentId":1,"title":"1.3"},
    {"id":6,"parentId":4,"title":"1.2.1"},
    {"id":7,"parentId":4,"title":"1.2.2"},
    {"id":8,"parentId":4,"title":"1.2.3"},
    {"id":9,"parentId":null,"title":"3"},
    {"id":10,"parentId":9,"title":"3.1"},
    {"id":11,"parentId":10,"title":"3.1.1"},
    {"id":12,"parentId":11,"title":"3.1.1.1"},
    {"id":13,"parentId":11,"title":"3.1.1.2"},
    {"id":14,"parentId":11,"title":"3.1.1.3"},
    {"id":15,"parentId":13,"title":"3.1.1.2.1"}
];

function NodeItem(data) {
    this.data=data;

    var container=document.createElement("li"),
        title=container.appendChild(document.createElement("div"));

    title.innerHTML=this.data.title;

    this.element=container;
} NodeItem.prototype={
    // lazy children element creation - not all nodes have children
    getChildrenElement:function () {
        return this._childElement = this._childElement || this.element.appendChild(document.createElement("ul"));
    }
};

// convert all nodes to NodeItem instance
var nodeCollection=treeData.map(function (node) { return new NodeItem(node); });

// for faster lookup, store all nodes by their id
var nodesById={};
for (var i=0;i<nodeCollection.length;i++) nodesById[nodeCollection[i].data.id]=nodeCollection[i];

var rootNodeItemsContainer=document.createElement("ul");

// the magic happens here:
// every node finds its parent (by the id), and it's being adopted by the parent's children element
// that, actually, builds the tree, before it's in the document
// all root nodes are appended to a root container which is appended to an element on the document
for (var i=0;i<nodeCollection.length;i++) {
    var node=nodeCollection[i];
    var parentElement=node.data.parentId ? nodesById[node.data.parentId].getChildrenElement() : rootNodeItemsContainer;
    parentElement.appendChild(node.element);
}

document.body.appendChild(rootNodeItemsContainer);
* { font-family:lucida grande, arial; font-size:11px; }

ul {
    xpadding:3px;
    border:1px solid #aaa;
}
    ul li {
        padding:5px;
        background-color:#eee;
    }
        ul li > div { padding:3px; xmargin-bottom:5px; background-color:#ccc; }
        ul li > div + ul { margin-top:5px; }
        ul li ul { margin-left:15px; }